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#21
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The centrifugal force generated by a rotor blade
is (W*r*rpm^2)/2900 W is the blade weight. r is the distance from the hub center to the CG of the blade |
#22
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Thanks for posting the formula. Let me see if I understand it correctly. For the hypothetical small helicopter: Blades are 10' long and the cg is half the length (no tip weights). R would be 5' plus the distance from the center of the shaft to the blade mounts. I'll call R as being 5.5' in this example. I'll say the blades are 25 lbs each and the RPM is 600 (450 MPH tip speed). FORCE = (W * R * RPM^2) / 2900 = (25 * 5.5 * 600^2) / 2900 = 17069 lbs. This is assuming that the units are supposed to be lbs and feet. The result is less than I thought, but still pretty impressive. By adding 2 lb tip weights, the CG force increases to about 23,500 lbs. That's a pretty big jump, but the biggest jumps obviously come with the RPM. Did I do it right? Dennis. (Hennie) wrote: The centrifugal force generated by a rotor blade is (W*r*rpm^2)/2900 W is the blade weight. r is the distance from the hub center to the CG of the blade Dennis Hawkins n4mwd AT amsat DOT org (humans know what to do) "A RECESSION is when you know somebody who is out of work. A DEPRESSION is when YOU are out of work. A RECOVERY is when all the H-1B's are out of work." To find out what an H-1B is and how they are putting Americans out of work, visit the following web site and click on the "Exporting America" CNN news video: http://zazona.com/ShameH1B/MediaClips.htm |
#23
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Hi, I was wondering if there was a simplified formula for working out
centrifugal force with a constant mass rotor. Unfortunately I can't make sence of it, what is the constant 2900 derived from? When using, F= MV^2/r F= force M= mass V= velocity r= radius By summing each calculation -- say at r=1m, 'X'm/s,M=1Kg r=2m 'X'm/s,M=2Kg and so on .(the smaller the increments the better) The end result is not even close to the formentioned formula. Where have I gone wrong? Cheers Cam (excuse the metric system) "Hennie" wrote in message om... The centrifugal force generated by a rotor blade is (W*r*rpm^2)/2900 W is the blade weight. r is the distance from the hub center to the CG of the blade |
#24
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Just guessing, but your formula uses Velocity and his uses RPM. The 2900 is probably due to the conversion of RPM to velocity in Miles Per Hour. V = (2*R*RPM)/28 (where units are V=Miles Per Hour, R=Feet) Also, your formula is apparently using Kg's and M's instead of Feet and pounds. Then again, I may be totally wrong as CAC is from South Africa and they use the metric system too. (I know this because I did a search for apartments in South Africa and all the square 'footage's were in square meters.) It would help if somebody would say for sure what the units are. Dennis. "Cam" wrote: Hi, I was wondering if there was a simplified formula for working out centrifugal force with a constant mass rotor. Unfortunately I can't make sence of it, what is the constant 2900 derived from? When using, F= MV^2/r F= force M= mass V= velocity r= radius By summing each calculation -- say at r=1m, 'X'm/s,M=1Kg r=2m 'X'm/s,M=2Kg and so on .(the smaller the increments the better) The end result is not even close to the formentioned formula. Where have I gone wrong? Cheers Cam (excuse the metric system) "Hennie" wrote in message om... The centrifugal force generated by a rotor blade is (W*r*rpm^2)/2900 W is the blade weight. r is the distance from the hub center to the CG of the blade Dennis Hawkins n4mwd AT amsat DOT org (humans know what to do) "A RECESSION is when you know somebody who is out of work. A DEPRESSION is when YOU are out of work. A RECOVERY is when all the H-1B's are out of work." To find out what an H-1B is and how they are putting Americans out of work, visit the following web site and click on the "Exporting America" CNN news video: http://zazona.com/ShameH1B/MediaClips.htm |
#25
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IN CLARIFICATION TO THE ABOVE:
THAT WAS NOT "DONALD TRUMP'S AGUSTA THAT WAS LOST IN THE ACCIDENT UP IN NEW JERSEY. THAT AIRCRAFT WAS LEASED THAT DAY FROM PARAMOUNT AVIATION. TRUMP HAD FIVE (5) OF HIS L A R G E HELICOPTERS SITTING IN THE HANGAR ON THE DAY THAT THE LEASED AIRCRAFT WAS LOST. I WAS THE CHIEF INSPECTOR FOR TRUMPS HELICOPTER OPERATIONS AT THE TIME SO YOU CAN TAKE THIS INFO TO THE BANK. HIS AGUSTA 109 WAS IN MAINTENANCE THAT DAY AND WAS UNAVAILABLE. THE BLADE THAT FAILED HAD A "FORGING LAP": LEFT IN THE M/R/B SPAR SINCE MANUFACTURE WHICH CREATED A "STRESS RAISER", EVENTUALLY A CRACK, AND THE REST IS HISTORY. For the rest of the commenters, now with many composite blades out there a better record can probably be expected although no great inspection methods have yet been developed for composites. Metal blades departed aircraft many many times, hence Sikorsky's "BIM" indicators on the blade roots. Hundreds of thousands od pounds of centrifugal force and cracked blades will always present a problem, huh? |
#27
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Whooops, I used the radius instead of the CoG of one blade (approx 1/2
radius). Now it works, far easier than my approach. Thanks. ps/ I like to use both metric and imperial as well, it comes in handy when building international space stations (I'm sure) Cheers Cam |
#28
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Its probably the same formula used to calculate how fast the space station must rotate in order to create artificial gravity. Now if the space station actually did that, it would be really cool. Dennis. "Cam" wrote: ps/ I like to use both metric and imperial as well, it comes in handy when building international space stations (I'm sure) Cheers Cam Dennis Hawkins n4mwd AT amsat DOT org (humans know what to do) "A RECESSION is when you know somebody who is out of work. A DEPRESSION is when YOU are out of work. A RECOVERY is when all the H-1B's are out of work." To find out what an H-1B is and how they are putting Americans out of work, visit the following web site and click on the "Exporting America" CNN news video: http://zazona.com/ShameH1B/MediaClips.htm |
#29
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Forgive my ignorance, but I need some clarification on your clarification. Describe exactly what a 'forging lap' is. What do I look for when inspecting a blade? Can it be seen outright, or is an X-ray necessary? Also, I thought that composite blades still used a metal spar. Is this not correct. If not, please describe their construction. Dennis. "Bob" wrote: I WAS THE CHIEF INSPECTOR FOR TRUMPS HELICOPTER OPERATIONS AT THE TIME SO YOU CAN TAKE THIS INFO TO THE BANK. HIS AGUSTA 109 WAS IN MAINTENANCE THAT DAY AND WAS UNAVAILABLE. THE BLADE THAT FAILED HAD A "FORGING LAP": LEFT IN THE M/R/B SPAR SINCE MANUFACTURE WHICH CREATED A "STRESS RAISER", EVENTUALLY A CRACK, AND THE REST IS HISTORY. For the rest of the commenters, now with many composite blades out there a better record can probably be expected although no great inspection methods have yet been developed for composites. Metal blades departed aircraft many many times, hence Sikorsky's "BIM" indicators on the blade roots. Hundreds of thousands od pounds of centrifugal force and cracked blades will always present a problem, huh? Dennis Hawkins n4mwd AT amsat DOT org (humans know what to do) "A RECESSION is when you know somebody who is out of work. A DEPRESSION is when YOU are out of work. A RECOVERY is when all the H-1B's are out of work." To find out what an H-1B is and how they are putting Americans out of work, visit the following web site and click on the "Exporting America" CNN news video: http://zazona.com/ShameH1B/MediaClips.htm |
#30
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Unfortunately, my clarification, specifically as to the cause of the
Agusta109 main rotor blade separation is in error. In that particular case, I was informed that at manufacture too much bonding material was applied to a weight that is bonded inside of the spar to achieve balance to manufacturing tolerances. That excess bonding material was "scraped" out leaving a tooling mark that eventually led to the crack. Now to briefly answer your questions: A "Forging Lap" is a flap of metal that should not be present after a forging or hammering type of process. Those spars are not forged, they are extruded (pushed or pulled through a die). Typically, manufacturing defects are not as blatent as to be seen by the naked eye, and many times are inside of the spar requiring x-ray, eddy current, or some other form of non-destructive detection. Composite (meaning totally composite) main rotor blades do not have a metal spar. Some newer composite main rotor blades incorporate a carbon fibre reinforced plastic spar and are filled with a Nomex honeycomb material. The blades are corrosion and damage resistant. Sorry for my error. |
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